Index ⭢ Core ⭢ asmjit::OffsetFormat

asmjit::OffsetFormat Struct Reference [¶]

Provides information about formatting offsets, absolute addresses, or their parts. Offset format is used by both RelocEntry and Fixup. The illustration below describes the relation of region size and offset size. Region size is the size of the whole unit whereas offset size is the size of the unit that will be patched.

+-> Code buffer |   The subject of the relocation (region)  |
|               | (Word-Offset)  (Word-Size)                |
|xxxxxxxxxxxxxxx|................|*PATCHED*|................|xxxxxxxxxxxx->
                                 |         |
    [Word Offset points here]----+         +--- [WordOffset + WordSize]

Once the offset word has been located it can be patched like this:

                              |ImmDiscardLSB (discard LSB bits).
                              |..
[0000000000000iiiiiiiiiiiiiiiiiDD] - Offset value (32-bit)
[000000000000000iiiiiiiiiiiiiiiii] - Offset value after discard LSB.
[00000000000iiiiiiiiiiiiiiiii0000] - Offset value shifted by ImmBitShift.
[xxxxxxxxxxxiiiiiiiiiiiiiiiiixxxx] - Patched word (32-bit)
            |...............|
              (ImmBitCount) +- ImmBitShift

Public Members

Members

OffsetType _type

uint8_t _flags

uint8_t _region_size

uint8_t _value_size

uint8_t _value_offset

uint8_t _imm_bit_count

uint8_t _imm_bit_shift

uint8_t _imm_discard_lsb

Member Functions

Accessors

OffsetType type() const noexcept

bool has_sign_bit() const noexcept

uint32_t flags() const noexcept

uint32_t region_size() const noexcept

uint32_t value_offset() const noexcept

uint32_t value_size() const noexcept

uint32_t imm_bit_count() const noexcept

uint32_t imm_bit_shift() const noexcept

uint32_t imm_discard_lsb() const noexcept

void reset_to_simple_value(OffsetType type, size_t value_size) noexcept

void reset_to_imm_value(OffsetType type, size_t value_size, uint32_t imm_bit_shift, uint32_t imm_bit_count, uint32_t imm_discard_lsb) noexcept

void set_region(size_t region_size, size_t value_offset) noexcept

void set_leading_and_trailing_size(size_t leading_size, size_t trailing_size) noexcept

OffsetType OffsetFormat::type() constnoexcept[¶]

Returns the type of the offset.

bool OffsetFormat::has_sign_bit() constnoexcept[¶]

Returns whether the offset is encoded as an absolute value of the offset with additional field(s) that represent the sign (AArch32 U/N fields in the opcode).

If true, the offset itself is always positive and a separate U/N field is used to indicate the sign of the offset (usually U==1 means ADD, but sometimes N==1 means negative offset, which implies SUB).

uint32_t OffsetFormat::flags() constnodiscardnoexcept[¶]

Returns flags.

uint32_t OffsetFormat::region_size() constnodiscardnoexcept[¶]

Returns the size of the region/instruction where the offset is encoded.

uint32_t OffsetFormat::value_offset() constnodiscardnoexcept[¶]

Returns the offset of the word relative to the start of the region where the offset is.

uint32_t OffsetFormat::value_size() constnodiscardnoexcept[¶]

Returns the size of the data-type (word) that contains the offset, in bytes.

uint32_t OffsetFormat::imm_bit_count() constnodiscardnoexcept[¶]

Returns the count of bits of the offset value in the data it's stored in.

uint32_t OffsetFormat::imm_bit_shift() constnodiscardnoexcept[¶]

Returns the bit-shift of the offset value in the data it's stored in.

uint32_t OffsetFormat::imm_discard_lsb() constnodiscardnoexcept[¶]

Returns the number of least significant bits of the offset value, that must be zero and that are not part of the encoded data.

void OffsetFormat::reset_to_simple_value(
OffsetType type,
size_t value_size
)noexcept[¶]

Resets this offset format to a simple data value of data_size bytes.

The region will be the same size as data and immediate bits would correspond to data_size * 8. There will be no immediate bit shift or discarded bits.

OffsetType OffsetFormat::_type[¶]

Type of the offset.

uint8_t OffsetFormat::_flags[¶]

Encoding flags.

uint8_t OffsetFormat::_region_size[¶]

Size of the region (in bytes) containing the offset value, if the offset value is part of an instruction, otherwise it would be the same as _value_size.

uint8_t OffsetFormat::_value_size[¶]

Size of the offset value, in bytes (1, 2, 4, or 8).

uint8_t OffsetFormat::_value_offset[¶]

Offset of the offset value, in bytes, relative to the start of the region or data. Value offset would be zero if both region size and value size are equal.

uint8_t OffsetFormat::_imm_bit_count[¶]

Size of the offset immediate value in bits.

uint8_t OffsetFormat::_imm_bit_shift[¶]

Shift of the offset immediate value in bits in the target word.

uint8_t OffsetFormat::_imm_discard_lsb[¶]

Number of least significant bits to discard before writing the immediate to the destination. All discarded bits must be zero otherwise the value is invalid.